In Logic Pro and Logic Express, you can play compressed audio formats such as AAC, Apple Lossless, and MP3 directly in the Arrange window. Because these files require less disk space, you might think that they would also require less processor and disk drive bandwidth to play back. However, directly playing compressed audio may require more of your computer's resources than playing back an equivalent number of uncompressed audio tracks. This could result in lower track counts.
In some situations, you may get better performance by converting your compressed audio tracks to AIFF or WAVE files.
To do so, select the relevant regions in the Arrange window and choose Arrange > Audio > Convert Regions to New Audio Files. A file selector will appear, allowing you to choose a destination and file format for the converted files.